Control of Underwater Actuators Using Ambient Pressure

ABSTRACT

A device for controlling an underwater actuator by using an ambient pressure potential at the operating depth may include a chamber including a first cavity, a second cavity and a third cavity; the first cavity including a gas at a first pressure including one of at surface atmospheric pressure, lower than surface atmospheric pressure, or a vacuum; the second cavity including a first fluid at a second pressure including at least one of at underwater ambient pressure or higher then underwater ambient pressure and being connected to a underwater fluid supply; the third cavity including a second fluid at a third pressure including at least one of underwater ambient pressure or higher than the underwater ambient pressure and being connected to the actuator.

FIELD OF THE INVENTION

The present invention relates to actuators and more particularly tounderwater actuators.

BACKGROUND

Underwater actuators may be required to be operated quickly. Actuatorsthat use control fluids require a pressure source that is higher thanthe ambient pressure at the operating depth in order to operate. Thepressure sources include pumps and gas charged accumulators. High flowpumps are required to operate high flow demand fluid actuators. However,accumulators may lose efficiency due to adiabatic discharge under highflow demands. As water depth increases, these devices become lessefficient which is undesirable.

Existing designs have focused on increasing the efficiency of thepositive pressure portion of the system that acts on the actuator pistonand have ignored the potential to use the pressure generated at a depthas a source to operate the actuator. This focus has resulted in usingeither (or a combination of larger pumps, accumulators with higher gaspre-charge pressures, changing the pre-charge gas to helium instead ofnitrogen, adding accumulators or increasing accumulator working volumecapacity by using depth compensated accumulators in deep water. In deepwater operations, these solutions decrease efficiency and reliability,add weight (by adding larger pumps or more accumulators), increaselogistics issues (using helium instead of nitrogen as the pre-chargedgas) or add complexity and potential for seal leakage due to cycling(depth compensated accumulators).

SUMMARY

A device for controlling an underwater actuator by using an ambientpressure potential at the operating depth may include a chamberincluding a first cavity, a second cavity and a third cavity; the firstcavity including a gas at a first pressure including one of at surfaceatmospheric pressure, lower than surface atmospheric pressure, or avacuum; the second cavity including a first fluid at a second pressureincluding at least one of at underwater ambient pressure or higher thanunderwater ambient pressure and being connected to a underwater fluidsupply; the third cavity including a second fluid at a third pressureincluding at least one of underwater ambient pressure or higher than theunderwater ambient pressure and being connected to the actuator.

The difference in pressure between the first cavity and the secondcavity generates a pressure differential moving a piston of theactuator.

The chamber includes a fourth cavity may include a fluid at a fourthpressure being at one of at underwater ambient pressure or slightlyabove underwater ambient pressure.

The chamber may include a piston connecting between the first cavity andfourth cavity.

The device may block fluid in the actuator preventing the actuator frommoving.

The device may include a hydraulic supply cooperating with an umbilicalto form an open loop system where return fluid is exhausted to theenvironment.

The hydraulic supply may be an underwater hydraulic power supplyoperating in a closed loop configuration where the fluid is reusedinstead of exhausting it into the environment.

The device may include a bulkhead with seals that separates the firstcavity and the third cavity.

The device may include a piston with a seal located in both the firstcavity and the third cavity

The device may include a rod connecting the pistons in each of the firstcavity and the third cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich, like reference numerals identify like elements, and in which:

FIG. 1 illustrates a circuit diagram for a subsea actuator of thepresent invention;

FIG. 2 illustrates another circuit diagram for the subsea actuator ofthe present invention;

FIG. 3 illustrates a cross-sectional view of the subsea actuator of thepresent invention;

FIG. 4 illustrates another circuit diagram for the subsea actuator ofthe present invention;

FIG. 5 illustrates a another cross-sectional view of the subsea actuatorof the present invention.

DETAILED DESCRIPTION Control of Underwater Actuators Using AmbientPressure

This invention takes advantage of the fluid column which may be a watercolumn or other appropriate fluid and which may create a higherunderwater ambient pressure at a predetermined depth than at the surfaceof the fluid. A chamber with one cavity containing a gas at surfacepressure, near vacuum or a vacuum uses the difference between underwaterambient pressure and surface pressure to operate an actuator. When onechamber cavity is connected to one side of an actuator piston it cancreate a pressure differential on the piston caused by the differencebetween underwater ambient pressure at the operating depth and surfacepressure, or less, in the chamber. The pressure differential created onthe actuator piston can be used to either operate an underwater deviceor operate it with less pressure above underwater ambient than wouldpreviously be required using a pressure source such as accumulatorsand/or pumps alone.

This invention uses a difference between the pressure generated by thewater column and a chamber containing pressure at the surface, vacuum ornear vacuum to generate a lower than ambient pressure on one side of anactuator piston. The pressure differential causes the piston to move.Movement of the piston operates the actuator.

The invention includes, but is not limited to:

1.) A fluid chamber or chambers which may include several cavities withdifferent fluids. One cavity may include gas at atmospheric pressure,near vacuum or vacuum. Other cavities may include the operating fluidsat various pressures.

2.) An Underwater actuator which may be operated by fluids.

3.) Control valves which may direct fluids and isolate parts of thesystem.

4.) A pressure source, pump, accumulator or both.

5.) Pressure compensated Fluid Reservoir

6.) Piping or passageway which may distribute fluids in the system

This invention describes methods and apparatus whereby an underwaterfluid pressure source may be used to move a piston to a position thatplaces the underwater actuator into a first position or a secondposition or another position. A second chamber which may be below thefirst chamber may include a cavity that is initially at surface pressureabsolute (or below as in a vacuum) and may include an inert gas, air ora vacuum in the cavity at the surface. The pistons of the first andsecond chambers may be connected together with a rod. The pressuredifferential between the ambient pressure and the pressure lower thanambient pressure in the gas (or vacuum) cavity of the chamber mayprovide the pressure differential and the potential to create a force onthe piston to operate the underwater actuator. As depth increases, thepressure differential also increases, making the device more efficientas water depth increases. If accumulators or pumps are used togetherwith the methods and apparatus described, a lower demand for pressuremay result and flow from the accumulators, or pumps, as depth mayincrease. The method and apparatus described therefore may reduce theamount of accumulator stored capacity on the underwater equipment andcan reduce the required pump size.

Referring to the drawings, FIG. 1 illustrates a circuit diagram of adevice. Using an underwater actuator 24 as an example, prior tooperating the actuator 24, the Valve 12 may be used on the surfacebefore deployment model to supply a predetermined quantity of fluid,plus a margin of fluid to a first Cavity 1 in Chamber 23 to permit theunderwater actuator 24 to operate to between both A and B positions.Chamber 23 may also be fabricated in two or more pieces being connectedby rod. Valve 12 which may be connected to cavity 1 may also be used tofill or drain Cavity 1 underwater. Valves13 a and 13 b may be used forhydraulic intervention by a remotely operated valve ROV to move Pistons17 and 18 to predetermined positions while the system is underwater. Afourth Cavity 4 in Chamber 23 may be purged with inert gas or air at oneatmosphere at the surface, or a vacuum in Cavity 4 may be introducedprior to deployment underwater. Cavity 1 and a second cavity 2 andpassageway 20 may be initially filled with fluid. When the hydraulicsystem (not shown) may be operating and the device may be underwater,the actuator 24 may be placed in position A by opening Valve 6 to supplyfluid to Cavity 2 and moving the Piston 18 in the chamber upwards (asshown on the drawing) and pressurizing the passageway 20 between cavity1 of Chamber 23 and Cavity 10 of Actuator 24. The pressurized fluidapplied to Cavity 10 of actuator 24 moves the actuator Piston 17 of theactuator 24 to position A. Cavities 10 and 1 finally reach theequilibrium pressure of the hydraulic system. Valve 6 may be then closedlocking the piston 18 and trapping fluid in Cavity 2. Check Valve 16 isa secondary device to prevent fluid from back flowing out of Cavity 2into Reservoir 9 via Valve 6 when Valve 6 is off. Chambers 10 and 1 maythen be hydraulically locked preventing the Piston 17 of the actuator 24from moving to position B. Cavity 2 may be at a pressure that resiststhe force generated by the pressure in Cavity 1 and the pressure ofcavity 4 may be below ambient by being gas filled. The pressuredifferential between Cavity 1 and 4 may close the actuator 24 when Valve8 is open, directing the fluid in Cavity 2 to the pressure compensatedreservoir 9 slightly above ambient pressure. This pressure differentialcauses the pressure in Cavity 1 and 10 to decrease to below ambient,moving the actuator 24 to position B. Valve 5 may be used to move thepiston 17 in actuator 24 to Position B. Check Valve 15 prevents fluidfrom bypassing to the Reservoir 9 during operation of Valve 5. WhenValve 5 is not active, it connects Chamber 11 to the Reservoir 9 whichis slightly above ambient pressure. A third Cavity 3 in Chamber 23 isconnected to the Reservoir 9. Its function is to reduce the pressuredifferential between Cavity 2 and 4 extending the life of the piston rodseals 32 between the two cavities. Check Valve 34 on reservoir 9 placesa back pressure on return fluid keeping the pressure in the line and allcomponents connected preventing the fluid in the environment (such asseawater) from entering the system and contaminating the fluid.

The previous description describes an open loop hydraulic system wherethe fluids are supplied from an external source such as an umbilical andthe excess fluid in the return line is exhausted into the environment.

Another method and apparatus of fluid supply is shown in FIG. 2 wherethere is included an underwater hydraulic power unit (HPU) 25 on theunderwater equipment and maybe powered by electricity or othercomparable devices, either underwater or from the surface. Instead ofexhausting fluid into the environment, the return fluid may be recycled.Fluid may be initially stored in reservoir 9. During operation, usedfluid may return to the reservoir 9 and is directed to Valve 31 andFilter 30 to the suction side of the hydraulic power unit HPU 25. Fluidmay be pumped to a higher pressure by the pump 25 and may pass throughthe check valve 27 and Filter 26 before the fluid may be directed to thesupply passageway 19 to be used by the system. Relief Valve 28 may limitthe pressure in the passageway 19 and may be a primary method ofpressure control for positive displacement pumps or a safety device forpressure compensated pumps (not shown) commonly used underwater

FIG. 3 describes the Chamber 23 which include the piston seals 33 androd seals 32.

Another method and apparatus of fluid supply is shown in FIG. 4.

FIG. 5 describes the Chamber 23 which include the piston seals 33 androd seals 32 without Cavity 3.

The invention describes methods and a device whereby a fluid pressuresource applied to a first chamber causes a piston in that chamber topush fluid out of another chamber and into the underwater actuator body.This fluid may be used to move the piston in the actuator. A secondchamber below the first is initially at one atmosphere pressure absoluteand contains an inert gas (or air) at surface pressure (14.7 psiabsolute) or a vacuum (0 psi absolute). The pistons of the first andsecond chambers are connected together with a rod or the chamber may beconstructed as one assembly. The hydraulic valve that directs fluid tothe first chamber is locked closed to prevent the pistons and rod frommoving after the underwater actuator is in one position. The pressuredifferential between the ambient seawater pressure and the lower surfacepressure in the gas filled chamber provides the potential to generate apressure differential to close the underwater actuator. As water depthincreases, the pressure differential also increases resulting in apotentially higher actuator operating force.

The chamber 23 that contains the surface atmospheric source and theoperating fluids may be one aspect in the invention. A pressure sourcemay charge (pressurized) and operate the chamber. Other parts of thesystem, such as valves and piping (passageways) may be used to supplyand direct flow to and from this chamber. These devices can beconfigured as described or can vary depending on the requirements of theunderwater system.

The chamber can be produced by machining the parts and assembling them.The parts are made from metals or plastics compatible with theenvironment. Standard elastomeric seals on the piston(s) may be used toseal the cavities from each other. The same manufacturing and assemblytechniques used to manufacture hydraulic cylinders may be used toproduce the chamber and the cavities within it. The balance of the partsrequired can be procured using readily available parts and assembled bypersons familiar with the art.

The circuit described shows one way the chamber can be installed in theunderwater system. A single chamber can be used to operate manyactuators or can operate only one. Multiple chambers can also be used invarious combinations.

The methods and apparatus described may be relevant to all underwateroperations and maybe useful specifically in deep water in underwatermilitary, scientific and commercial oil and gas operations. Typicalexamples in the offshore oil and gas industries may include operation ofequipment for drilling, coring, production and all interventionoperations.

The system may be used in any underwater environment where a pressuredifferential can be generated or any environment where there may be apressure differential generated by ambient conditions such as inside apressure vessel or in a submarine.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed.

1) A device for controlling an underwater actuator by using an ambientpressure potential at the operating depth, comprising: a chamberincluding a first cavity, a second cavity and a third cavity; the firstcavity including a gas at a first pressure being one of at lower thansurface atmospheric pressure or a vacuum; the second cavity including afirst fluid at a second pressure including at least one of at underwaterambient pressure or higher then underwater ambient pressure and beingconnected to a underwater fluid supply the third cavity including asecond fluid at a third pressure including at least one of underwaterambient pressure or higher than the underwater ambient pressure andbeing connected to the actuator; wherein the difference in pressurebetween the first cavity and the second cavity generates a pressuredifferential moving a piston of the actuator. 2) A device forcontrolling an underwater actuator by using an ambient pressurepotential at the operating depth as in claim 1, wherein the chamberincludes a fourth cavity including a fluid at a fourth pressure being atone of at underwater ambient pressure or slightly above underwaterambient pressure. 3) A device for controlling an underwater actuator byusing an ambient pressure potential at the operating depth as in claim2, wherein the chamber includes a piston separating the first cavity andfourth cavity. 4) A device for controlling an underwater actuator byusing an ambient pressure potential at the operating depth as in claim1, wherein the device blocks fluid in the actuator preventing theactuator and piston from moving. 5) A device for controlling anunderwater actuator by using an ambient pressure potential at theoperating depth as in claim 1, wherein the device includes a hydraulicsupply cooperating with an umbilical to form an open loop system wherereturn fluid is exhausted to the environment. 6) A device forcontrolling an underwater actuator by using an ambient pressurepotential at the operating depth as in claim 1, wherein the hydraulicsupply is an underwater hydraulic power supply operating in a closedloop configuration where the fluid is reused instead of exhausting tointo the environment. 7) A device for controlling an underwater actuatorby using an ambient pressure potential at the operating depth as inclaim 1, wherein the device includes a bulkhead with seals thatseparates the first cavity and the third cavity. 8) A device forcontrolling an underwater actuator by using an ambient pressurepotential at the operating depth as in claim 1, wherein the deviceincludes a piston with a seal located between the first cavity and thethird cavity 9) A device for controlling an underwater actuator by usingan ambient pressure potential at the operating depth as in claim 1,wherein the device includes a rod connecting a piston between the firstcavity and the third cavity. 10) A device for controlling an underwateractuator by using ambient pressure potential at the operating depth asin claim 5, wherein a reservoir is included that is at a pressureslightly higher than ambient pressure, said compensated reservoirprevents fluid in the environment from entering the parts of the fluidsystem when used in an open loop system.